An extruded part looks simpler to buy than a moulded one. There is no expensive mould, the cross-section fits on one sheet of paper, and the factory quotes by the metre or by the kilogram. Then the first delivery arrives: the profile measures correctly at one end and not at the other, the lengths have shrunk since they were cut, and the “virgin PVC” turns out to contain a proportion of reground scrap nobody mentioned.
Extrusion is a continuous process, and that changes what you have to agree. This article covers the four things to fix before a Vietnamese extruder quotes your pipe, profile or sheet: the die and its trials, how dimensions are measured, what the compound may contain, and how long lengths are packed.
💬 Have an extruded profile or pipe you want made in Vietnam? Send us the cross-section drawing and the annual length and we will help you turn it into an enquiry that several extruders can quote on the same basis.
What exactly are you buying: pipe, profile or sheet?
Pipe, profile and sheet run on similar extruders but are specified, measured and packed differently, so say which one you are buying and, for pipe, which product standard it must meet.
A factory that runs pressure pipe all day may quote your window profile using pipe assumptions about tolerances and testing, so say which family you mean.
| Pipe | Custom profile | Sheet | |
|---|---|---|---|
| What defines it | A product standard plus size and pressure class | Your drawing | Thickness, width, surface finish, flatness |
| Tooling | Die and sizing sleeve, often from the factory’s existing range | A new die and calibrator built for your section | Flat die, usually existing; rolls set the surface |
| Typical dispute | Wall thickness at the thin point, pressure test failures | Section out of tolerance, bow and twist over length | Thickness variation across the width, surface marks |
| Usual testing | Dimensions, pressure, reversion, as the standard requires | Dimensions and fit, plus whatever you specify | Thickness map, appearance, any property you specify |
For water and pressure pipe, the international references are ISO 4427-2:2019 for polyethylene pipes and ISO 1452-2:2009 for PVC-U pipes. If your market uses a national or regional standard instead, name that one; the point is that a pipe enquiry without a standard leaves the factory to choose the wall thickness, the material class and the test regime for you.
1. The die: budget for trials, not just for steel
A new profile die is rarely right first time; it is corrected over several trial runs, so agree how many trials the tooling price includes and who pays for the rest.
A custom profile needs a die, which shapes the melt, and a calibrator, which holds the section while it cools. Melt does not flow evenly — thick sections flow faster than thin ones, and the profile swells and shrinks as it leaves — so the die maker corrects the flow channels after each trial until the cooled section matches the drawing.
Put these points in the enquiry so each quotation answers them:
- Number of trial runs included in the die price, and the charge for each additional trial if the buyer changes the drawing.
- Sample length and quantity sent to you from each trial, and whether a cut section photograph with measurements comes with it.
- Who designs the die — the extruder in house, or an outside die shop. If outside, ask which party corrects it during trials.
- Cooling-line length and line speed assumed. The same die gives different results at a different speed; the speed in the quotation should be the speed at approval.
- Co-extrusion. If the profile has a second material — a soft seal lip, a coloured cap layer, a recycled core — say so at the start. It needs a second extruder and a different die.
Ownership, marking and release of the die and calibrator are the same questions as for any mould and are covered in tooling and mould ownership in Vietnam. One extrusion-specific point: a die is set up around a particular extruder and cooling line, so moving it to another factory usually means a new set of trials, even when you own the steel.
2. Dimensions: where, when and how to measure
Extruded dimensions change as the material cools and relaxes, so the drawing must say where on the section and how long after extrusion each dimension is measured, or two honest inspectors will get two results.
Plastic continues to shrink after cutting, so the factory’s in-line gauge, its QC bench and your incoming inspection can disagree for reasons that have nothing to do with quality.
Settle four things on the drawing or the inspection plan:
- Conditioning before measurement. How long after extrusion, and at what temperature, the section is measured. Without it, lengths in particular will argue.
- Measuring method for the section. For pipe, ISO 3126:2005 sets out how to measure diameters, out-of-roundness, lengths and wall thickness — name it and the factory’s mean outside diameter means the same as yours. For a profile, agree whether the section is checked by callipers, an optical comparator, a cut-section scan or a go/no-go gauge built for the mating part.
- Features along the length. Bow, twist and straightness only appear over a full length laid on a flat surface. State the length over which they are measured and the maximum allowed.
- Cut length. State the tolerance and the temperature at which length is measured; a long length cut warm can be short by the time it reaches you.
For pipe, longitudinal reversion — the shrinkage that appears when a cut length is reheated, showing how much stress was frozen in — is tested to ISO 2505:2023. Pressure pipe is also tested for resistance to internal pressure under ISO 1167-1:2006. Whether these apply, and at what parameters, comes from the product standard you named, not from the factory’s habit.
Metal-style tolerances copied onto every dimension lead to refusals or unrealistic acceptances. Mark the few dimensions that control the fit and let the rest follow a general tolerance; the method is in CNC machining in Vietnam.
💬 Unsure which dimensions on your section really control the fit? We can review the drawing with you before it goes to quotation, as part of sourcing from Vietnam. Tell us about the part.
3. The compound: what is in it, and how much is recycled
An extruded part is made from a compound, not a pure resin; the stabiliser, the filler and the share of recycled or reground material are what change between factories and between lots, so they belong in the specification.
PVC is never extruded as polymer alone. It carries a heat stabiliser, lubricants, impact modifier and often a mineral filler such as calcium carbonate. Filler is normal in rigid PVC, but its level changes stiffness, impact strength and surface quality, and it is the easiest lever to pull when a price must come down.
Specify, at minimum:
- Base polymer and grade, or an approved list of grades, as with moulded parts.
- Filler limit, where it matters, and how it will be checked — for example by ash content on a sample.
- Stabiliser system. If the parts are going to the EU, lead in PVC is restricted under REACH Annex XVII, entry 63, as amended by Commission Regulation (EU) 2023/923: articles made from PVC may not be placed on the market if lead is at or above 0.1% by weight of the PVC material, with effect from 29 November 2024, and with later dates for some recovered PVC. Ask for a written statement of the stabiliser type, not an assumption.
- UV and colour. For outdoor parts, the UV package; for colour, the reference sample, the light it is judged under, and how lot-to-lot variation is accepted.
Three kinds of “recycled”, and why the difference matters
“Recycled” covers three different things, and an order should say which are allowed:
| Material | Where it comes from | What you can know about it | Usual position |
|---|---|---|---|
| In-house regrind | The factory’s own start-up scrap and edge trim of the same compound | Composition is known, but heat history adds up with each pass | Often allowed up to a written maximum |
| Post-industrial recyclate | Scrap bought from other converters | Composition depends on the source; mixing grades is possible | Allowed only if you approve the source |
| Post-consumer recyclate | Collected used products, sorted and reprocessed | Most variable; contaminants and legacy additives possible | Specified deliberately, with testing, or excluded |
Co-extrusion gives a middle path some buyers use: a recycled core with a virgin skin, so the surface and colour stay consistent. If you or your customer need to claim recycled content, EN 15343:2007 sets out how recycled plastics are traced through the supply chain and how recycled content is calculated; ask whether the extruder’s recyclate supplier can provide records on that basis. If the parts touch food, recycled plastic is subject to separate rules in the destination market — confirm them there before you allow any.
Whatever you decide, write the share and the type down. A purchase order that says nothing about regrind does not forbid it. Which material documents to ask for at which stage is covered in quality documents to request from a Vietnamese parts supplier.
4. Marking, packing and loading long lengths
Extrusions are long, light and easy to deform, so the packing method decides whether a part that left the factory in tolerance arrives in tolerance.
Damage is mostly mechanical and thermal: lengths bowed by uneven support, pipes ovalised at the bottom of a stack, profiles scratched by each other, and thin sections softened under load in a hot container.
Agree in writing:
- Lengths and bundling. Lengths chosen to suit the container you will use, the number per bundle, and how bundles are strapped without crushing the section.
- Support. Timber or plastic spacers at stated intervals for straight lengths; crates for profiles with fragile legs; maximum stacking height for pipe.
- Protection. Protective film on visible faces of profiles and sheet, and end caps on pipe to keep dirt and insects out.
- In-line marking. Pipe and many profiles can be printed continuously on the line. Use it: standard, size, production date and line or lot code printed at regular intervals along the length make complaints traceable to a shift.
- Coils. Small-diameter polyethylene pipe can be supplied in coils; agree the minimum coil diameter so the pipe is not kinked.
Each bundle label should carry the part number, drawing revision, lot code and length, matching the packing list. Inspection of bundles before loading — counting, sampling for dimensions, checking the packing method itself — can be built into pre-shipment inspection and AQL.
The enquiry checklist for an extruded part
An extrusion quotation can only be compared with another when each extruder has the same section, the same compound rules, the same measurement plan and the same packing.
- Section drawing with critical dimensions, general tolerance and datum; for pipe, the product standard and class.
- Compound: polymer and grade, filler limit, stabiliser statement, UV and colour reference, and which recycled material is allowed and how much.
- Die trials included and who corrects the die.
- Measurement plan, cut length and tolerance, marking on the part.
- Annual length or weight, typical order, packing and loading method.
Price basis differs too. Some extruders quote per metre, some per kilogram with an assumed weight per metre. If a quotation is per kilogram, ask for the theoretical weight per metre behind it and how weight variation is handled; otherwise two “identical” prices can cover different amounts of material. The commercial normalisation is in comparing Vietnamese supplier quotations, and the stages from trial sample to approved production in sample approval stages. For moulded plastic parts, see injection moulding in Vietnam; for moulded rubber seals and mounts, rubber moulded parts from Vietnam.
💬 For each project we find, vet and manage the Vietnamese extruder that fits the section, the material and the volume. Send us the drawing and we will tell you what we would ask the factories first.
Frequently asked questions
1. Why do the factory’s measurements and mine disagree?
Usually because the part was measured at different times, temperatures or positions. Plastic shrinks after extrusion and the section can vary along the length. Agree the conditioning time, the measuring method and the measuring position in writing, then compare like with like.
2. How many die trials should I expect?
It depends on the section. A simple solid profile may settle quickly; thin legs, hollow chambers and tight tolerances need more rounds. Rather than guessing, ask each extruder to state how many trials its tooling price includes and what an extra trial costs.
3. Can I ban regrind completely?
You can, and for some parts you should. Be aware that a total ban removes a normal way for the factory to use its own clean scrap, which may show in the price. Many buyers allow in-house regrind of the same compound up to a written maximum and exclude bought-in recyclate unless approved.
4. If I own the die, can I move it to another extruder easily?
You can move it, but expect new trials. A die is tuned to a particular extruder and cooling line, so the new factory will usually need to run it in before production. The ownership and release terms themselves belong in the tooling agreement.
5. Which standard should my pipe meet?
The one your market and application require. ISO 4427-2 for polyethylene water pipe and ISO 1452-2 for PVC-U pressure pipe are common international references, but many countries use national standards. Name the standard and class in the enquiry so the factory does not choose them for you.
Sources: ISO 4427-2:2019; ISO 1452-2:2009; ISO 3126:2005; ISO 2505:2023; ISO 1167-1:2006; EN 15343:2007; Commission Regulation (EU) 2023/923 amending REACH Annex XVII, entry 63. Checked on 19 October 2026.
More industrial sourcing guides: Rubber Moulded Parts From Vietnam: Seals, O-Rings and Mounts · Aluminium Extrusion in Vietnam: Alloy, Die, Finish and Cutting · Making Moulds and Dies in Japan for an Overseas Factory. All guides by category are on the industrial sourcing page.